Method and apparatus for monitoring the electrode support of an arc furnace

ABSTRACT

The physical pressure contact, and hence electrical connection, between the stinger and electrode support stub of an arc furnace is monitored continuously by an electric circuit interconnecting the stinger and the electrode lifting rod, the electric circuit including a switch actuator which is responsive to a predetermined magnitude of voltage drop across the stinger-stub connection to effect disconnection of the high current arc source from across the stinger and electrode crucible.

United States Patent 1191 1111: 3,868,473 Dimick Feb. 25, 1975 METHOD AND APPARATUS FOR 3,495,018 2/19 70 Jackson et al. 13/9 x MONITORING THE ELECTRODE SUPPORT OF AN ARC FURNACE [75] Inventor: Royal H. Dimick, Albany, Oreg. [73] Assignee: Teledyne Wah Chang Albany,

- Albany, Oreg.

[22] Filed: Dec. 20, 1973 [21] Appl. No.: 426,552

'52 us. c1 13/13, 13/12, 13/34 [51] Int-Cl. H05b 7/12 [58] Field oi Search 13/9, 15, 16,18, 12, 13, 13/34 ['56] References Cited UNlTED STATES PATENTS 3,354,254 11/1967 Jackson et a1. 13/9 A The physical pressure contact, and hence electrical connection, between the stinger and electrode support stub of an arc furnace ismonitored continuously by an Primary Examiner-R. N. Envall, Jr. Attorney, Agent, or FirmOliver D. Olson ABSTRACT electric circuit interconnecting the stinger and the electrode lifting rod, the electric circuit including a switch actuator which is responsive to a predetermined magnitude of voltage drop across the stingerstub connectionto effect disconnection of the high current are source from across the stinger and electrode crucible.

v 7 Claims, 1 Drawing Figure 12 ill METHOD AND APPARATUS FOR MONITORING THE ELECTRODE SUPPORT OF AN ARC FURNACE BACKGROUND OF THE INVENTION This invention relates to arc furnaces for the melting and purification of metals, and more particularly to method and means for preventing arc damage to the stinger-electrode stub connection of an arc furnace.

In conventional arc furnaces the electrode to be melted is connected to a stub which, in turn, is supported detachably by a lifting rod extending from a hydraulic ram or other power means operable to move the ram vertically relative to the crucible containing the electrode. A tubular stinger encircles the lifting rod and is arranged to be brought into physical pressure contact with the stub to provide therebetween an electrical connection which completes the electric circuit of a source of high current which is connected across the stinger and crucible.

In the operation of such are furnaces it is a frequent occurrence that the physical contact between the stinger and stub is decreased to the extent that excessive voltage drop across the contact results in severe arcing and consequent melting or other destruction of the stinger, or stub, or both. This necessitates replacement of one or both of these components, and such replacement requires shut-down of the furnace and the involvement of considerable time and personnel to effect the replacement. These factors of labor and lost production time are reflected in significantly increased costs of production. No means has been provided heretofore to avoid this problem.

SUMMARY OF THE INVENTION In its basic concept, this invention involves the continuous monitoring of the voltage drop across the pressure contact between the stinger and electrode support stub of an arc furnace by means responsive to a predetermined magnitude of voltage to effect disconnection of the high current arc source.

It is by virtue of the foregoing basic concept that the principal objective of this invention is achieved; namely, to overcome the aformentioned problem associated with the operation of arc furnaces.

A further important object of this invention is the provision of apparatus of the class described which, is of simplified construction, is adaptable for use with a wide variety of types of arc furnaces and is precise and faithful in its operation.

The foregoing andother objects and advantages of this invention will appear from the following detailed description, taken in connection with the accompanying drawing of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWING The single figure is a foreshortened view in vertical elevation, partly in section, of an arc furnace having associated therewith monitoring apparatus embodying the features of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes merely of illustration, the drawing shows in somewhat schematic form a typical type of arc furnace for the melting and purification of metal. The are furnace includes a hollow, vertically elongated crucible 10 of electrically conductive material. The crucible serves to receive freely therein an electrode 12 of metal to be melted. The electrode is supported at its upper end by an electrically conductive stub 14 usually secured to the electrode by welding, as illustrated.

The stub is supported detachably from the lower end of an elongated lifting rod 16. The detachable connection illustrated is of conventional design, and includes a post 18 projecting upward from the stub and provided at its upper end with an enlarged head 20. This head is adapted to be received removably in a socket 22 formed in the lower end of the rod, whereupon cam- -actuated locking balls 24 are extended into the socket under the head to secure the connection.

The upper end of the lifting rod 16 is attached to a piston which is reciprocative vertically in a cylinder 26 supplied with fluid under pressure selectively at its opposite ends through conduits communicating with a source (not shown) of fluid under pressure. The cylinder is supported for vertical adjustment by such means as the piston rods 28 of a pair of elongated fluid pressure cylinders 30.

Freely surrounding the lifting rod is a vertically elongated, hollow stinger 32 of electrically conductive material. The stinger is supported for vertical adjustment with the cylinder 26, as by means of peripherally spaced connecting rods 34 secured at their upper ends to an electrical insulator 36 on the cylinder and at their lower ends to the upper end of the stinger.

The lower end of the stinger is provided with an enlarged shoulder 38 the lower face of which confronts the upper face of the stub 14 for mutual pressure contact, and hence electrical contact, over a substantially large surface area. It is this pressure contact that is monitored by the apparatus of this invention.

A source of high current is connected to the arc furnace. In the typical installation illustrated, the opposite ends of the secondary of a power transformer 40 are connected through conductors 42 and 44 to the crucible 10 and to the stinger 32, respectively. The transformer primaryvis connected releasably to the terminals 46 of a source of high current through relay contacts 48 the coil 50 of which is connected to a source of electric potential for selective activation.

In accordance with this invention, automatic means is provided for disconnecting the source of high current from between the crucible and stinger when the pressure contact between the stinger shoulder 38 and stub 14 is decreased to the extent at which a predetermined magnitude of voltage drop occurs across the contact. In the general concept of this invention, this means is provided by a switch actuator connected across the stinger and stub and responsive to a predetermined magnitude of voltage drop across the latter to effect disconnection of the high current supply from across the crucible and stinger.

In the embodiment illustrated the switch actuator comprises an electric circuit which includes the relay coil 50. Thus, one terminal 52 of the source of electric potential is connected to one end of the coil and the opposite end of the coil is connected through a normally open, momentary push-button start switch 54, a manually resettable relay contact 56 and a normally closed, momentary push-button safety switch 58 to the other terminal 60 of the supply. A holding circuit for the coil is provided by the relay contact 62 connected across the normally open start switch 54.

The contact 56 is associated with a relay coil 64 which is connected across the stub 14 and stinger 32. In the embodiment illustrated, this connection is provided conveniently by connecting one end of the coil 64 to the stinger 32 and the other end of the coil to the lifting rod 16. Since the lifting rod is connected electrically to the stub through the detachable coupling provided by the post 18, the electrical connection is effectively made to the stub.

The relay coil 64 preferably is of the adjustable type,-

whereby opening of its associated contact 56 can be achieved upon the attainment of a selected predetermined magnitude of voltage drop across the stinger and stub. For convenience of adjustment, a voltmeter 66 may be connected across the coil.

The assembly of. relay coil 64, associated contact 56 and voltmeter 66, bounded by the broken line, conveniently is provided by commercial sources. One such assembly is available as General Electric relay Type 1953, Catalog No. 50-195312PZPZ2JBF.

It will be understood, of course, that various other types of switch actuators may be utilized in place of the type illustrated. One such type utilizes a photocell, the light beam of which is interruptable by the indicator arm of a voltmeter at adjustable positions throughout the range of the latter. Upon such interruption of the light beam at a predetermined magnitude of voltage, the photocell functions to operate a relay to disconnect the high current sourcd from across the crucible and stinger.

In the operation of the system described hereinbefore, the operator depresses the start switch 54 to complete the electric circuit of relay coil 50. Transfer of its associated contacts 48 from the open positions illustrated connects the high current source to the arc furnace, and closure of the associated contact 62 completes the holding circuit which bypasses the start switch 54. The operator thus may release the latter.

In the event the pressure contact between the stub 14 and stinger shoulder 38 decreases to an extent that a selected predetermined magnitude of voltage drop, typically about l.5 volts, occurs across the pressure contact, the relay coil 64 is energized to effect opening of its associated contact 56. The electric circuit of the relay coil 50 thus is opened, whereupon the associated contacts 48 transfer to the open'condition illustrated, disconnecting the high current source from across the crucible and stinger, thereby preventing damage to the stinger, or stub, or both.

After the pressure contact between the stinger and stub has been restored to proper magnitude, the, open contact 56 is manually reset to the closed position illustrated and the start switch 54 once again closed to initiate operation of the arc furnace.

From the foregoing it will be appreciated that the present invention provides simplified and economical means by which continuous monitoring of the pressure contact between the stinger and electrode support stub prevents serious damage thereto and thus substantially eliminates the lost production time and other cost factors heretofore incurred with this problem.

It will be apparent to those skilled in the art that various changes may be made in the type, number and arrangement of parts described hereinbefore without departing from the spirit of this invention.

Having now described my invention and the manner in which it may be used, I claim:

1. In an arc furnace wherein an electrode support stub and stinger are supported for relative movement into mutual pressue contact and a source of high current is connected releasably across the stinger and an electrode-containing crucible, the method of controlling automatically the application of said high current across the stinger and crucible, comprising electrically connecting across the stub and stinger an electric circuit including a switch actuator responsive to a predetermined magnitude of voltage drop across said pres- I sure contact to effect disconnection of the source of high current from across the stinger and crucible.

2. The method of claim 1 wherein the high current source is connected releasably across the stinger and crucible through an electric relay having an electric circuit, the method including connecting in said electric relay circuit a switch associated with said switch actuator.

3. Themethod of claim 1 wherein the stub is supported by a lifting rod and the electrical connection to the stub is made by connection to the lifting rod.

4. In an arc furnace having an electrode support stub and stinger relatively movable into mutual pressure contact and a source of high current connected releasably across the stinger and an electrode-containing crucible, apparatus for controlling automatically the application of said high current across the stinger and crucible, comprising switch means in the electric circuit of said source of high current, and switch actuating means connected across the stub and stinger and operable in response to a predetermined magnitude of voltage drop across said stub and stinger to effect opening of the switch means.

5. The apparatus of claim 4 wherein the stub is supported by a lifting rod and the switch actuating means is connected across the lifting rod and stinger.

6..The apparatus of claim 4 wherein the switch means includes a relay coil having an electric circuit, and the switch actuating means comprises a relay having a switch contact connected in the electric circuit of the relay coil of the switch means.

7. The apparatus of claim 6 wherein the switch actuating relay is adjustable to effect operation of its switch contact at selective magnitudes of voltage drop across the stub and stinger. 

1. In an arc furnace wherein an electrode support stub and stinger are supported for relative movement into mutual pressue contact and a source of high current is connected releasably across the stinger and an electrode-containing crucible, the method of controlling automatically the application of said high current across the stinger and crucible, comprising electrically connecting across the stub and stinger an electric circuit including a switch actuator responsive to a predetermined magnitude of voltage drop across said pressure contact to effect disconnection of the source of high current from across the stinger and crucible.
 2. The method of claim 1 wherein the high current source is connected releasably across the stinger and crucible through an electric relay having an electric circuit, the method including connecting in said electric relay circuit a switch associated with said switch actuator.
 3. The method of claim 1 wherein the stub is supported by a lifting rod and the electrical connection to the stub is made by connection to the lifting rod.
 4. In an arc furnace havIng an electrode support stub and stinger relatively movable into mutual pressure contact and a source of high current connected releasably across the stinger and an electrode-containing crucible, apparatus for controlling automatically the application of said high current across the stinger and crucible, comprising switch means in the electric circuit of said source of high current, and switch actuating means connected across the stub and stinger and operable in response to a predetermined magnitude of voltage drop across said stub and stinger to effect opening of the switch means.
 5. The apparatus of claim 4 wherein the stub is supported by a lifting rod and the switch actuating means is connected across the lifting rod and stinger.
 6. The apparatus of claim 4 wherein the switch means includes a relay coil having an electric circuit, and the switch actuating means comprises a relay having a switch contact connected in the electric circuit of the relay coil of the switch means.
 7. The apparatus of claim 6 wherein the switch actuating relay is adjustable to effect operation of its switch contact at selective magnitudes of voltage drop across the stub and stinger. 